[clang] [clang][Sema] Add buffer-size checks for unistd I/O functions (PR #224979)

[Denys Fedoryshchenko via cfe-commits]

nuclearcat wrote:

Rebased onto current main, replaced per-call lookup-table construction with static descriptors: 17 Sema tests pass, and the 100,000-call benchmark improved from 24.9% to 2.1% overhead versus main.

https://github.com/llvm/llvm-project/pull/224979